Photodiodes (InGaAs for short-wavelength infrared and Si for visible and near infra-red applications) demonstrate high sensitivity. However they are limited by read-out noise and their quantum efficiency is limited to unity (i.e. 1 carrier per absorbed photon). In view of the absence of photoconductive gain in photodiodes, APDs (avalanche photodiodes) have been developed to provide gain via carrier multiplication effects. The gain in these devices is on the order of 100 to 1000 carriers per absorbed photon. The technological challenges in integrating these structures to common image sensors and low-cost detectors is the high operating bias required (on the order of 100's of V) and additional layers required to suppress leakage currents and prolong the device lifetime from degradation due to the high applied bias. Moreover, these devices are not monolithically integrable to CMOS electronics due to the different growth process required for APDs.